The present invention relates to polymeric labels and, more specifically, to polymeric labels that can be applied using water-based adhesives.
Polymeric labels are applied to a wide variety of bottles and containers to provide, for example, information about the product being sold or to display a trade name or logo. Polymeric labels can provide various advantageous characteristics not provided by paper labels, such as durability, strength, water resistance, curl resistance, abrasion resistance, gloss, translucence, and others.
For example, U.S. Pat. No. 5,194,324 issued to Poirier teaches the use of an opaque, biaxially oriented polymeric label stock structure. This structure includes an opaque thermoplastic polymer matrix core layer, a high-gloss medium-density polyethylene first skin layer, and a second thermoplastic polymer skin layer with an adhesive on its surface. The core layer has a stratum of closed-cell voids that gives the structure its opacity. Poirier discloses that the adhesive could be pressure sensitive, activated by water (for hydrophilic adhesive coatings), or activated by solvent (for adhesive coatings that are more hydrophobic). However, label substrates of this kind are unsuitable for some types of conventional manufacturing techniques.
For example, the application of paper labels to glass and plastic containers using water-based adhesives is still one of the most prevalent labeling techniques presently used. Consequently, there are many existing machines that have been installed for this type of labeling technique. These cut-label techniques using water-based adhesives work well with paper-based labels applied to glass, plastic, or metal substrates, because the wet adhesive wicks into the paper label, which breathes. This release of the adhesive moisture through the labels allows the adhesive to fully dry. This technique does not work, however, on polymeric labels, as described in U.S. Pat. No. 5,194,324, because the polymeric label does not permit wicking of the moisture from the adhesive when used as a decal on a window or a patch label on a container. This can make the polymeric labels prone to “swimming” or moving from the desired label location during down stream processing.
U.S. Pat. No. 6,306,242 issued to Dronzek attempts to address this problem by applying a relatively heavy hydrophilic polymeric layer (0.40 to 13 g/m2) to the plastic label to absorb a portion of the water from the water-based adhesive. However, hydrophilic coatings or a coextruded hydrophilic layer tends to absorb water from the atmosphere in humid conditions thereby hindering the ability of the hydrophilic layer to bond with the adhesive layer. In addition, the hydrophilic layer can lose water to the atmosphere in dry conditions. This gain and loss of moisture can cause the label to curl thereby hindering label application. Moreover, humidity-induced curl can create severe processing problems when converting roll stock into sheets.
U.S. Publication 2001/0036542 A1 submitted by Marks describes a multi-layer, metallizable, white opaque film suitable for use in forming metallized plastic labels for bottles and other containers. The publication describes a structure containing an internal core layer, preferably free of void-creating additives, and opposed outer skin layers. The publication further describes that one of the outer skin layers is a non-voided layer having a surface treated to receive a metal layer thereon and the opposed outer skin layer includes an amount of a void creating additive to provide sufficient porosity for the absorption of an aqueous cold glue adhesive of the type employed to adhere a label to a container. Similarly, multi-layer cavitated structures described in U.S. application Ser. No. 09/770,960, published as U.S. 2002/0146520 on Oct. 10. 2002. and metallized refinements of this structure (U.S. Application filed by ExxonMobil on Dec. 30, 2002 which is a continuation-in-part of U.S. application Ser. No. 10/098,806, published as U.S. 2003/0172559 on Sep. 18, 2003) describe a thermoplastic label comprising a closed-cell core and a non-cavitated printable surface and an open-cell opposing surface with enough porosity for the absorption of an aqueous cold-glue adhesive of the type employed to adhere a label to a container. These films perform well as labels when attached to containers with aqueous-based cold glues. However, these films may present difficulties in manufacturing and processing. For example, these films may perform poorly in presses which require substrates in sheet form. In particular, the conversion of these films from roll stock into sheets, and the stacking of the sheets and subsequent feeding through a printing press may present difficulties.
There is therefore a need in the art for a polymeric label that can be applied using conventional techniques involving a water-based adhesive without the drawbacks associated with thick hydrophilic coatings/layers. There is a further need in the art for a polymeric label/water-based adhesive combination which provides good initial tack and allows complete drying of the adhesive in less time than conventional polymer label/water-based adhesive combinations while still allowing for efficient processing during sheeting, printing, and bottling operations.